Workers in a variety of environments, such as hospitals, factories, and institutions of learning may be exposed, depending on the circumstances, to a variety of noxious gases at low concentrations. A number of such commonly encountered vapors are listed by Saxe, I. N., Dangerous Properties of Industrial Materials, 5th Ed., Van Nostrand Reinhold Co., N.Y. (1979) as particular problems in the technologically sophisticated environments of developed countries. Also, lists of hazardous trace substances present in work places and in the general environment in the U.S. are published periodically by the Occupational Safety and Health Administration and by the Environmental protection Agency in the Federal Register. Contaminating gases include ethylene oxide, formaldehyde, sulfur dioxide, carbon monoxide, hydrogen sulfide, nitrogen oxides, peroxides, acidic gases, arsine and phosphine, ozone, and halogens. This list, of course, is not limiting or all inclusive but includes those substances that may be found in reasonably low concentrations, i.e., in the ppm or ppb ranges, where prolonged exposure constitutes a hazard.
It is well understood currently that persons in environments where even permitted levels of the above gases exist must be monitored for exposure. The time-average concentration or dose applied over time is particularly important since this parameter correlates strongly with the effect on the exposed individual. Accordingly, there have been many attempts to design devices which are capable of assaying total exposure to an individual or to a particular location. Many of these methods involve bulky collection systems such as cartridges providing passage through adsorbents such as charcoal or solvents, or complex-to-manufacture diffusion devices. See, for example, NIOSH Manual of Analytical Methods, 2nd Ed, Pt 1-NIOSH Monitoring Methods NIOSH 77-157-A, and U.S. Pat. Nos. 3,985,017 and 3,924,219. The portable portions of these devices are simply for collection and storage, and the procedures for signal development and readout require skilled personnel and independent instrumentation.
In most instances, the collection device is, in fact, separate from the detection system. The desired material is extracted from the device, and the chemistry which permits detection of the target gas by development of a color or by other means is performed separately. This generally involves the use of instrumentation with concomitant investment of time and facilities, capital investment, and commitment of skilled personnel.
The only devices presently commercially available which attempt to integrate the detection chemistry with the collection device involve complex and expensive collector systems attached to development reagents enclosed in plastic bags. (See U.S. Pat. No. 4,208,371.) The plastic bags are then squeezed into a configuration suitable for reading in a colorimeter. In many cases additional reagents are required which must be freshly made in the laboratory. No device currently exists which is capable of accurately assessing total dosage or time weighted average exposure at low levels that is simple, inexpensive, and capable of immediate quantitative readout by non-expert personnel.